Dave.
Sounds like Rich os pointing you in the right direction. While he does all the leg work and sorts you out
, have a butchers at
www.cclonline.com, they are normally very good on price and are up near Ikea, so you can pick up your order and save on postage.
As mentioned, check out the 'today only' page on
www.scan.co.uk, they often have value bundles which are motherboard, memory and chip at really good prices.
I always aim to spend around £100 on a graphics card, as that generally gets you something that's really good, but obviously not the best that's out there. I always build my own PC's as I know what's in it then, I also always buy Asus motherboards. I once bought a cheap AsRock board and it was a complete nightmare....
PC's are a bit like the buggies really, would you buy a Ready To Run.... or build you own !